Method of stray compensation in tuned antennae



w. KAUTTER 2,109,536 METHOD OF STRAY COMPENSATION IN TUNED ANTENNAEMafch 1, 1938.

Filed Oct. 24, 1934 INVENTOR 1701/34/76: [407/259 BY L/ ATTORNEYPatented Mar. 1, 1938 UNITED STATES arcane METHOD OF STRAY COMPENSATIONIN TUNED ANTENNAE Wolfgang Kautter, Berlin, Germany, assignor toTelefunken Gesellschaft fiir Drahtlose Telegraphic in. b. 11., Berlin,Germany, a corporaf-ion of Germany Application October 24, 1934, SerialNo. 749,700 In Germany November 9, 1933 3 Claims.

In order that perfect reception may be insured in large cities and inorder that, to that end, stray and interfering actions present inbuildings may be eliminated, the suggestion has been made to mount ahigh aerial upon the top of a building located inside a district subjectto a little interference, and to statically shield the down leads to thereceivers. These down leads consist of high frequency cables whichcomprise a conduct tor and a conductive shield or envelope surroundingthe said conductor, the envelope being united with the ground terminalof the receiver, while the inner conductor is connected with the antennaterminal.

15 Now, it has been discovered that reception by no means is freest frominterference when the cable sheath or envelope, or the receiver casingis grounded. The reasons underlying this finding and fact shall beexplained hereinafter.

20 In the accompanying drawing Fig. 1 illustrates schematically areceiver and an associated antenna system which will serve to explainthe invention; Fig. 2 shows the system of Fig. 1 redrawn in a differentway but is electrically equiv- 35 alent thereto; Fig. 3 is a portion ofthe antenna system embodying one modification of the invention; and Fig.4 is a like portion of the antenna system but embodying a differentmodification of the invention.

9 Now, referring first to Fig. 1, A denotes an antenna, and the energypicked up by it is to be fed to the receiver R by way of the radiofrequency cable or down lead K. If the connection between the cable andthe receiver be properly made the shielding of the receiver is sointimately united with the envelope of the cable that the representationas shown in the drawing Will be admissible according to which thereceiver, as it were, is accommodated inside the cable.

40 The presupposition is that the cable fundamentally has been correctlyconstructed.

The current fed to the receiver R by way of the inner conductor of thecable flows up on the inside of the cable envelope and down again 45 onthe outside thereof. Incidentally its value becomes gradually smallerinasmuch as more and more flows off to the antenna by virtue of capacitybetween it and the envelope. In this way the current through the outerlayer of the en- 50 velope decreases as the distance from the antennaincreases. What may be remarked in this connection is that thedimensions of broadcast antennae are always small in contrast with thewave lengths so that it is permissible to regard 55 the strictlydistributed capacitances as concentrated or lumped, and to disregardinductances. In this manner the scheme shown in Fig. 1 is obtained.

An interferer S which, on the one hand, is grounded directly orcapacitively, on the other 5 hand is in coupling relationship, by reasonof the stray electric field around it, by way of the leakage capacitiesCla and CH0 (being of an'order of magnitude up to 30 micro-microfarads)with the antenna and the outside of the cable sheath. 10 The antenna andthe cable envelope are connected directly with earth throughcapacitances Cae and Clce, and there further exists between antenna andoutside of the cable envelope 2.

direct capacitance Gala.

In Fig. 2 the capacitances just enumerated are shown in a different way,and it can be seen that they are contained in the arms of a Wheatstonebridge. In one diagonal is included the interfering E. M. F. S., in theother the receiver connected by way of the cable, and in parallelrelation thereto the capacitance Cale between antenna and outsideenvelope of the cable. By

choosing suitable dimensions a state of bridge balance is establishablein which the receiver is uncoupled or neutralized in regard to theinterfering source.

Now, what is suggested according to this invention is to make one ormore of the existent capacities variable, and to thus insureoutbalancing for at least one of the major disturbing sources. I

So far as the solution of the idea underlying the invention is concernedthere exist a great many fundamentally known possibilities. If the bal-'ance is to be produced by increasing Cite, then a rotary condenser isincluded between cable and earth. On the other hand, that is to say,when Cke is already toohigh the capacitance between antenna and earthmust be raised, and this is accomplishable, e. g., as shown in Fig. 3 bythat the inner conductor is brought out directly at the receiver and isunited with earth by way of a rotary condenser. Another possible schemeis indicated in Fig. 4. In this arrangement Cke and Cae aresimultaneously varied by the agency of the differential condenser D.

What I claim is:

1. An aerial system comprising the combination of an antenna, a lead-inextending from the antenna to a radio communication device, a metallicshield surrounding said lead-in and being coupled to earth by thenatural capacity be tween said shield and earth and a variable conitybetween the local voltage source and said shield multiplied by thecapacity between the antenna and ground whereby disturbances from saidlocal voltage source are prevented from affecting said radio device.

3. An antenna system comprising an antenna lead, shielding means forsaid lead, and a differential condenser for capacitively connecting saidlead and said shielding means to ground.

WOLFGANG KAU'ITER.

